There are conventionally known a traction-type self-propelled vehicle that is removably coupled to a carriage on which pieces of work, luggage and the like are laid and runs in a self-propelled manner along a predetermined route with the aid of guide means such as magnetic information or the like set on a floor surface while towing the carriage, an onboard-type self-propelled vehicle that is integrally coupled to a carriage on which pieces of work, luggage and the like are laid and runs in a self-propelled manner along a predetermined route with the aid of the guide means, and the like.
In recent years, there has been an ever-increasing tendency to make use of self-propelled vehicles for conveyance as described above. There is a demand for speed-up (to about 80 m/min) for the sake of efficiency enhancement. At the same time, there is also a demand for a guarantee of safety from speed-up. When an obstacle or the like is detected on a predetermined route while a self-propelled vehicle for conveyance runs at high speed, it is indispensable to swiftly stop the self-propelled vehicle for conveyance on the predetermined route.
Thus, a method of controlling a stop of a self-propelled vehicle for conveyance of related art will be described.
The self-propelled vehicle for conveyance of related art is equipped with an obstacle detection sensor capable of detecting an obstacle in a non-contact manner, a stop control device that decelerates/stops, on the basis of the detection by the obstacle sensor, a pair of left and right driving wheels that rotate independently of each other, and a safety bumper that shuts off the transmission of power to the self-propelled vehicle for conveyance upon contact with the obstacle.
In the stop control method of related art, first of all, the obstacle detection sensor detects an obstacle located at a predetermined distance during the running of the self-propelled vehicle for conveyance.
After that, on the basis of the detection by the obstacle detection sensor, the stop control device sets command rotational speeds for the pair of the left and right driving wheels to those in a stop mode (0 rpm for both the left and right driving wheels). The self-propelled vehicle for conveyance is thereby gradually decelerated and stopped.
However, in the case where the self-propelled vehicle for conveyance runs at high speed, even when the stop control device sets the command rotational speeds for the respective driving wheels to those in the stop mode, a stop braking distance after the detection of the obstacle becomes long. Therefore, the self-propelled vehicle for conveyance cannot be stopped in front of the obstacle.
That is, in the stop control method of related art, the self-propelled vehicle for conveyance is naturally decelerated and stopped through stop control in the stop mode for the respective driving wheels, namely, through the setting of the command rotational speeds for the respective driving wheels to those in the stop mode (0 rpm for both the left and right driving wheels) and with the aid of the friction or the like between a floor surface and respective driven wheels of a carriage and the driving wheels of the self-propelled vehicle for conveyance. Therefore, especially when the self-propelled vehicle for conveyance runs at high speed, the stop braking distance of the self-propelled vehicle for conveyance after the detection of the obstacle becomes long, and the self-propelled vehicle for conveyance cannot be stopped in front of the obstacle.
Thus, in the stop control method of related art, when the self-propelled vehicle for conveyance runs at high speed, the transmission of the power to the self-propelled vehicle for conveyance is shut off to completely stop the self-propelled vehicle for conveyance as soon as the safety bumper of the self-propelled vehicle for conveyance comes into contact with the obstacle.
As described above, in the aforementioned method of controlling the stop of the self-propelled vehicle for conveyance of related art, when the self-propelled vehicle for conveyance is caused to run at high speed, the stop braking distance of the self-propelled vehicle for conveyance after the detection of the obstacle by the obstacle detection sensor is long, and the transmission of the power to the self-propelled vehicle for conveyance is shut off to completely stop the self-propelled vehicle for conveyance as soon as the safety bumper of the self-propelled vehicle for conveyance comes into contact with the obstacle. Therefore, especially in some cases including a case where a heavy object is laid on the carriage on the self-propelled vehicle for conveyance, a very dangerous situation lasts over a long zone from a spot corresponding to the detection of the obstacle to a spot corresponding to a complete stop of the self-propelled vehicle for conveyance resulting from its contact with the obstacle. Thus, in related art, the maximum speed of the self-propelled vehicle for conveyance is limited to guarantee safety.
Thus, as a related art for solving the aforementioned problem, Patent Document 1 describes that an electromagnetic brake (a mechanical brake) and an electric brake are both employed to shorten a stop braking distance of an automatic conveyance vehicle as emergency stop control for the automatic conveyance vehicle.    Patent Document 1: Japanese Patent Application Publication No. JP-A-1-26210